The present invention relates generally to the field of automated apparatus for handling electronic circuit components and, more particularly, to automated apparatus for use in the art of burning-in circuit components prior to their distribution and use. Still more particularly, the present invention is directed to the art of automated unloading of electronic integrated circuit (IC) packages from sockets on printed circuit (PC) boards and simultaneous sorting of the packages according to predetermined performance grades.
According to present practices, IC packages are mass-produced and installed in electronic circuits within highly sophisticated, complex and costly equipment. As with many mass-produced products, IC packages are prone to failure, in many cases within the first one thousand hours of operation. The complexity of the equipment within which such packages are installed makes post-installation failures highly undesirable. For example, when equipment reaches the final inspection stage of production, before failures are detected, the high level skills required for testing and repair add a significant cost to production expenses. Even more significantly, when the product has been installed in the field and a service technician must make warranty repairs, the costs thereby incurred can have a significant effect on profitability. As a result, manufacturers of electronic equipment are demanding ever greater quality and dependability in commercial grade IC packages.
Quality and dependability are enhanced substantially by detection of those IC packages likely to fail in the first few hours of operation, prior to installation of the packages in electronic equipment. One of the methods for detecting flawed IC packages is referred to as "burn-in". According to burn-in techniques, IC packages are stressed within their physical and electrical limits prior to installation, whereby those packages likely to become early failures in completed equipment can be discovered.
Burn-in involves placing a large number of IC packages on one or more PC boards ("burn-in boards"); placing the burn-in boards with the packages mounted thereon in a chamber whose environment, particularly temperature, is controllable; applying direct current (dc) biases to each package on each board in such a manner as to forward and reverse bias as many of the package's junctions as possible, and/or actively clocking each package to its maximum rated conditions, such application of dc biases and clock signals being accomplished substantially simultaneously to each package; removing the burn-in boards from the chamber after the IC packages have been subjected to the environmental condition of the chamber and the biases and clock signals for a designated period of time; and removing the IC packages from the burn-in boards.
A second method for improving quality control of the IC package subsequent to burn-in is to verify that the IC package functions according to its minimum rated specifications. Typically, each IC package is tested across a broad range of parameters and graded in quality according to its performance. Thereafter, the IC packages are sorted into groups according to the predetermined performance grades.
The burn-in and testing processes, however, although successful in reducing the expense of troubleshooting failed electronic equipment, are not themselves without expense. Substantial capital expenditures are necessary to purchase or construct burn-in chambers, burn-in boards, and test equipment. Personnel must be employed and trained to operate the equipment and to monitor the time-consuming processes. In some cases entire businesses have been built around performance of the burn-in and testing processes. Use of the processes and, consequently, the success of a business that provides such services, is dependent upon the cost effectiveness of burning-in and testing the IC packages vis-a-vis not burning-in or testing the IC packages but instead replacing those IC packages that fail after installation and use in the field.
One means for improving the cost effectiveness of the burn-in and testing processes is a reduction in labor costs. Accordingly, efforts have been made to automate the foregoing processes as much as possible. Several companies manufacture machines for loading IC packages into sockets on a burn-in board. See, for example, copending U.S. patent application Ser. No. 442,518, filed on Nov. 18, 1982, assigned to the assignee of the present application. Machines for unloading IC packages from the sockets on a burn-in board also have been constructed.
The assignee of the present application manufactures a Burn-In Board Device Unloader Model 1217, described generally in an advertising circular of the same title. The burn-in board to be unloaded is positioned on an inclined base with each column of IC packages aligned with a tapered lifting rod. Each lifting rod comprises a ramp-like base portion of gradually increasing depth and a carriage tube at the upper portion thereof. The lifting rod is inserted into a longitudinal channel formed in a socket providing access to the underside of an IC package. As the lifting rod moves along the longitudinal channel, on the underside of the column of IC packages, the IC packages are lifted sequentially from the sockets and fed by gravity along the carrier tube to plastic storage tubes. Several lifting rods are moved simultaneously by manual motion along the columns of sockets and IC packages, whereby an entire board may be unloaded in a single sweep of the arm.
Applicant is aware that IDEA, Inc. manufactures an automated burn-in board unloader. It is believed that the IDEA machine removes IC packages a row at a time from sockets by inserting a hook means between the socket and the IC package and moving the hook means perpendicularly away from the burn-in board so as to pull the IC package from the socket. The IC packages then are fed by gravity from the hook means to plastic storage tubes.
A wide variety of apparatus is available for performing the aforedescribed testing and sorting of IC packages after the burn-in process is completed (assuming that the burn-in process is to be performed). U.S. Pat. Nos. 3,587,852; 3,664,499; 3,727,757; and 3,896,935 show automated apparatus for testing and sorting IC packages. Typically, IC packages are fed serially from plastic storage tubes to a conveyor mechanism, whereby the IC packages are communicated sequentially to testing apparatus. Once the testing is completed, the IC packages are deposited in one of several containers according to the test results.
Thus, automated apparatus is available for loading IC packages onto burn-in boards, for burning in the IC packages, for unloading the burn-in boards and for testing and sorting the burned-in IC packages. In an effort to improve the efficiency of the foregoing quality assurance program, apparatus has been designed and constructed for burning in and simultaneously testing the IC packages, obviating the need for a separate test apparatus. If, however, the IC packages must be sorted into a plurality of grades as well, the improved efficiency derived from combining the burn-in and testing processes is lost as the IC packages are manually sorted according to the predetermined grades.
Hence, it should be apparent that maximum efficiency in the quality assurance program could be achieved through use of an automated apparatus capable of unloading a burn-in board and sorting the IC packages according to predetermined performance grades.